A reduction in carbon dioxide emissions has been recently more required to save resources and energy and to protect the environment. Accordingly, various ways for reducing carbon dioxide emissions of automobiles, such as weight saving and utilization of electric energy, have also been studied. To achieve these aims, tires for automobiles are required to have reduced rolling resistance so as to enhance fuel economy. Also, it is desired that tires have improved properties such as higher rubber strength.
Known methods for reducing rolling resistance include, for example, use of a silica formulation, reduction of the amount of filler, and use of filler with a little reinforcement. These methods, however, tend to reduce the strength of the rubber composition and deteriorate various properties.
Patent Literature 1 discloses a composition containing a butadiene rubber that contains 1,2-syndiotactic polybutadiene crystals, a modified butadiene rubber, and silica, thereby improving fuel economy and the like. Notwithstanding there still remains room for improvement in improving processability, rubber strength, fuel economy, and crack growth resistance in a balanced manner.